Method of and apparatus for controlling x-ray tubes.



|. LANGMUIR.

METHOD OF AND APPARATUS FOR CONTROLLING X-RAY TUBES. APPLICATION FILEDOCT. 29. 1913. RENEWED APR. 19. 1911.

1,251,388. Patented Dec. 25,1917.

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ED STATES PATENT OFFICE.

IBVmG WGMUIR, OE SCHENECTADY, NEW YORK, ASSIGNOE- TO GENERAL ELECT-BIGCOMPANY, A CORPORATION OF NEW YORK.

mrrron or arr Specification of Eetters Patent.

Patented Dec. 25, 1917.

Application flied October 29,1918, Serial No. 797,984. Renewed April 19,1917. Serial No. 163,315.

0 Apparatus for Controlling X-Ray Tubes,

of which the following is a specification.

The present invention relates to a system of connections for vacuumtubes of'the incandescent cathode type, such, for example, as the X-raytube described in Coolidge Patent 1,203,495 issued October 31,1916.

This "type of X-ray tube operates at extremely high vacua with a pure'ele tron discharge as contrastedwith Riintgen tubes formerly constructeddepending in their action upon the ionization of a residual gas. In oneof the modifications of this tube the cathode rays are focused by meansof a static focusing device, such as a. rim tube, or other conductivemember surroundmg the 'cathodeand establishin a static field radiallyabout the catho e. The focusing member appears to become staticallycharged by the electron emission of the cathode, and

thus modifies the static field in the tube,

which is controlling the motion of the cathode rays.

In accordance with myinvention the length of the focus of the cathoderays is valued at will, thus controlling the area of the focal spot orsurface by adjusting the distribution of potential in the static fielddirecting the cathode rays inwardly to a common point, or outwardly froma virtual focus. For example, by means of a source, of potential betweenthe cathode and the focusing device the intensity and polarity of thestatic field. may be' varied as hereinafter described.

In the drawings, Figure '1 illustrates diagrammatically a Ront'genraytube provided with a umdirectional source of potential between thecathode and static focusing means; Fig. 2 shows a Riintgen tube operatedfrom an alternatin current source and controlled: by a potential'whichfluctuates in synchronis'm with the current supply for the tube; vandFig. 3 shows another means for varying the focus.

I the essential parts of the tube comprise an Referring to Fig. 1 itwilLbe noted that envelop 1 of glass, or quartz, a cathode 2 and ananode 3, located opposite the cathode,

and serving also as a focal plate, or focal surface. The cathode, whichis a primary source of electrons, consists of a refractory conductor,preferably tungsten. Energy is supplied to incandesce the cathodethrough leadmg-in wires 4 and 5 from a battery 6 in series with avariable resistance 7.. The

anode consists of refractory metal, preferably tungsten. Around thecathode is located a short tube 8 also consisting of metal, for example,nickel, iron or tungsten representing one form of focusing device. Thesupports for the various parts such as the stem 9 for the cathode, a rod11) for the anode, and spring anchors 11 for, the focusing means havebeen only diagrammatically indicated, as they form no part of thepresent invention. Electrical current is supplied to the tube throughconductors 12 and 13 from a source of energy which may be a mechanicalrectifier, a high potential battery', or even an alternating currentsource, such as an induction coil or transformer. The source 14 issymbolic of any of the sources mentioned or their equivalents.

A source of potential 15 which has been diagrammatically indicated as adirect current dynamo, but mayalso be a battery, or even a static sourceof potential such as a glass plate static machine, is connected by meansof conductors 16 and 17 and a reversing switch 18 to the cathode and thefocusing member. By changing the switch blades from contacts 19 and 20to contacts 20 and 21, the polarity of the.source may be reversed. Thedegree of potential may be varied in an desired manner, as by varyingthe excitation of the field coil 22 of the generator, for example, bycutting in or out resistance 23 in the circuit of an energizing battery24, or in any other well understood manner. A resistance 25 is providedin circuit with the source of potential, which may be varied and alsoentirely shortcircuited as indicated.

When the focusing member 8 is connected to the cathode withoutinterposing any source of potential, one of the surfaceswhic may beplotted in space to include points of the same potential, will includethe tip of the filament and the outer edge of the focusing tube 8. Assuch equipotential surfaces approach the anode they become less concave.The electrons emitted by the filament when traveling from the cathode tothe anode, tend to move perpendicularly to these equipotential surfaces,and are thus directrim of the focusing member no longer are atthe samepotential. By making the posi- J tive potential high enough the focusingof hence on the hardness of the X-rays.

the rays may be entirely prevented, that is, the rays will divergeinstead of converge. By making the, potential negative with re- .spectto the focusing tube the focal area may be made smaller, or in otherwords,

sharpness ofthe focusing may be improved. a

The charge on the focusing member also has an effect on the resistanceof the tube ang positive charge decreasesthe hardness and anegative'charge increases the hardness in proportion to the potential ofthe charge.

The structure of the Rontgen ray tube shown in Fig. 2 is the same asthat shown in Fig. 1, but instead of a direct current source ofpotential for the focus control, analternate-source, for example, atransformer 28 is used. As has been indicated this transformer mayreceive current from the lines 27 which supply. current to thetransformer 26 connected to the main terminals of the 'X-ray tube. Thepotential in the transformer 26, therefore, will vary in synchronism andbe the same in polarity as the transformer 28. As in Fig. 1 a resistance29 and a reversing switch 30 is provided in the control circuitconnected to the secondary of the transformer 28.

The operation of the system described in Fig. 2 is similar to thatalready described in Fig. 1. Only the half waves of the supply currentwhich are negative with respect to the cathode 2 can pass through thetube. Because of this rectifying property of the tube, the alternatingpotential between the focusing device 8 and the cathode 2 operatessimilarly to a direct current source, as it only functionates for wavesof like polarity, the set of waves of opposite polarity beingsuppressed. The focal. area may be broadene or focusing entirelyprevented by connecting the positive terminal of the source of potential26110 the focusing device 8, the opposite terminal being connected tothe cathode, and in like manner the sharpness of focusing may beimproved by connecting the negative terminal of the source of potentialto the focusing member. In both the systems described in Figs. 1 and 2,the focusing may be varied by changing the degree of potentialas well asthe polarity.

For certain purposes focus control may be of the tube in theneighborhood of the focusing membeg' 8 which in this case consists ofmagnetlc material such asiron. By moving the member 8 away" from theanode 3 the length of thb focus may be increased and the focal areabroadened and conversely by movlength of the focus may be shortened andthe focal spot decreased. Obviously the shape of the equipotentialsurfaces is changed in this ma'nney.

Certain broad aspects of my invention described herein are claimed in acopendin renewal application Serial N 0. 84,242, filed March 14, 1916,which is involved in interference.

What I claim as new and desire to secure by letters Patent of the UnitedStates, is

1. In an electron discharge apparatus, a container, a cathode emittingelectrons independently of positive ionization, an anode, a conductivemember surrounding an axis passing through the cathode and anode, and

a source of potential connected between the cathode and said conductivemember, said apparatus being evacuated to a pressure so low that thefocusing of electrons in the space between the cathode and the anodeiscontrollable by an electric field.

2. The combination of a Riintgen ray tube comprising an evacuatedcontainer, an electron-emitting cathode, and a coiiperating anode, meansfor focusing the cathode rays, and means for establishing a static fieldradially about the cathode, and means for varying said field to vary thearea on a focal surface on which the cathode rays impinge to produceRiintgen rays.

3. An X-ray apparatus comprising an ing the focusing tube towardtheanodethe evacuated container, an incandescent cathode, a cobperatinganode, a device for modifying the static field near the, cathode, asource of potential between said cathode and said device and means forvarying said potential at will.

at. The combination with a Rdntgen ray,

tube having an electron-emitting cathode, and a focusing ringsurrounding the cathode, of a source of potential between said cathodeand focusing ring, means for varying said potential and means forreversing the polarity of said source at will.

5. The method of controlling the discharge emitted by the cathode of anelectrical vacuum discharge device which consists in establishing astatic field radially about the cathode causing the cathode rays to bediverted inwardly or outwardly, and

varyin the intensity1 of the static field to vary t e length of t efocusing.

6. The method of controlling the focusing of rays emitted by a cathodeof a Riintgen my device, which consists in establishing a. static fieldradially about the cathode to direct the rays inwardly or outwardly andva g the intensit and polari of said fiel to vary the de ection of sairays.

7. An electron-discharge apparatus comprisin the combination of acontainer; a catho e constituting a primary source of electrons, ananode, a conductive member Y uctive member and means for varying saidpotential at will.

In witness whereof, I have hereunto set :0 my hand this 27th day ofOctober, 1913.

IRVING LANGMUIB. Witnesses:

SAUL DUsnmN, HELEN Onronn.

